linux-kernel - Re: [RFC][PATCH v2 01/21] e820: cheat PMEM as DRAM

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Date:   Fri, 28 Dec 2018 11:27:44 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Fan Du <fan.du@...el.com>, KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yao Yuan <yuan.yao@...el.com>,
        Peng Dong <dongx.peng@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        Liu Jingqi <jingqi.liu@...el.com>,
        Dong Eddie <eddie.dong@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Zhang Yi <yi.z.zhang@...ux.intel.com>
Subject: Re: [RFC][PATCH v2 01/21] e820: cheat PMEM as DRAM

On Thu, Dec 27, 2018 at 11:32:06AM -0800, Yang Shi wrote:
>On Wed, Dec 26, 2018 at 9:13 PM Dan Williams <dan.j.williams@...el.com> wrote:
>>
>> On Wed, Dec 26, 2018 at 8:11 PM Fengguang Wu <fengguang.wu@...el.com> wrote:
>> >
>> > On Wed, Dec 26, 2018 at 07:41:41PM -0800, Matthew Wilcox wrote:
>> > >On Wed, Dec 26, 2018 at 09:14:47PM +0800, Fengguang Wu wrote:
>> > >> From: Fan Du <fan.du@...el.com>
>> > >>
>> > >> This is a hack to enumerate PMEM as NUMA nodes.
>> > >> It's necessary for current BIOS that don't yet fill ACPI HMAT table.
>> > >>
>> > >> WARNING: take care to backup. It is mutual exclusive with libnvdimm
>> > >> subsystem and can destroy ndctl managed namespaces.
>> > >
>> > >Why depend on firmware to present this "correctly"?  It seems to me like
>> > >less effort all around to have ndctl label some namespaces as being for
>> > >this kind of use.
>> >
>> > Dave Hansen may be more suitable to answer your question. He posted
>> > patches to make PMEM NUMA node coexist with libnvdimm and ndctl:
>> >
>> > [PATCH 0/9] Allow persistent memory to be used like normal RAM
>> > https://lkml.org/lkml/2018/10/23/9
>> >
>> > That depends on future BIOS. So we did this quick hack to test out
>> > PMEM NUMA node for the existing BIOS.
>>
>> No, it does not depend on a future BIOS.
>
>It is correct. We already have Dave's patches + Dan's patch (added
>target_node field) work on our machine which has SRAT.

Thanks for the correction. It looks my perception was out of date.
So we can follow Dave+Dan's patches to create the PMEM NUMA nodes.

Thanks,
Fengguang

>>
>> Willy, have a look here [1], here [2], and here [3] for the
>> work-in-progress ndctl takeover approach (actually 'daxctl' in this
>> case).
>>
>> [1]: https://lkml.org/lkml/2018/10/23/9
>> [2]: https://lkml.org/lkml/2018/10/31/243
>> [3]: https://lists.01.org/pipermail/linux-nvdimm/2018-November/018677.html
>>
>